Method for producing chromium or alloys of chromium



atented ept. it, 124.

BO it i ST'URE KALLING AND SVEN DAGOIBERT DANIELI, OF' TROLLHATTAN,

EIG', ASSEGNORS '1'0 AKTIEBOLAGET FERROLEGERINGAR, OF STOCKHOLM, SEN, A SIGHT-ST COMPANY LIDEITED.

' DUCING To all whom it may concern:

Be it known that we, Bo MICHAEL STURE KALLING and SVEN Daoonnn'r DANIELI, subjects or the King of Sweden, residing at Trollhattan, Sweden, have invented certain new and useful Improvements in Methods for Producing Chromium or Alloys of Chromium, of which the following is a specification.

The present invention relates to a method of producing chromium or alloys of chromium poor in carbon and silicon, and is an improvement in part upon that described in our co-pending application Serial No. 335,670, filed November 4, 1919. In said co-pending application we have described a process of manufacturing chromium alloys which consists in subjecting a chormium alloy rich in silicon, at a suitable temperature, to theoxidizing action of free oxygen blown in through the siliconohromium alloy while the latter is in molten condition. The principal object of the present invention is to provide a process in which the chromium contained in the end slag resulting from the process described in said co-pending application is utilized in a novel and practica manner.

Analysis made at various periods during the bessemerizin process, of samples of the slag and the a by simultaneously taken from the converter, have demonstrated the following facts: Samples taken during the early stage of the desilication process, that is, while the ,content of silicon in the alloy is high, Show that the content of chromium in the slag is low. On the other hand, samples taken ater on in the bessemerizing process, that is to say, after the content of silicon in the alloy has decreased, show the content of chromium in the slag to have correspondingl increased. By numerous tests of this c aracter it has been demonstrated beyond question that the content of chromium in the slag varies inversely with the content of silicon in the alloy. For instance, when the alloy shows a silicon content of 20%, the slag will be found to conmum Application filed May 4, 1921.

Serial No. 466,743.

tain a chromium content of approximately contain a chromium content of approximately And when the alloy contains a silicon content of 1%, the slag contains a chromium content of approximately We have also discovered that if, during the bessemerizing process, chrome ore is added to the charge under treatment, the

ratio of chromium content in the slag to the silicon content im the alloy is usually high only durin a comparatively short time, and that a ter supplying ore to the charge the ratio between the chromium content in the slag and the silicon content in the alloy will soon return to normal proportions, that is, to the proportions that would have been present if no.0re had been added. For instance, if'at the stage of the process when the silicon content is about 25%, at which time the converter slagis practically-speaking free from chromium, a quantity of ore is added which will cause a momentary raising of the chromium content of the slag to, say, 15%, and the process continued, it will be found that when the percentage of silicon in the alloy has decreased, for insta'noe,to15%, the chromium content of the slag will be only about 3%, which is the same content of chromium which would have been present if no ore had been added. These facts indicate that in carrying out the process set forth in our co-pending application hereinbefore referred to, a byproduct comprising a slag relatively rich in chromium is obtained, in addition to an alloy poor in carbon and silicon. This slag may, of course, be used as an initial material for producing a chromium alloy to be treated by bessemerizing, but is inferior for this pur ose. We have discovered that if, instea of adding chrome ore to the charge in the converter, a slag taken I from a converter during an advanced stage of desilication, when the chromium content of said slag is high, is added to another charge during'an earlier stage of desilication, the main part of said chromium content may be obtained as a chromium alloy,

if the Bessemer treatment of the last-mentioned chargeis interrupted at the stage when the proper balance of silicon content in the alloy and chromium content in: the slag is reached. Theoretically there is no reason why this procedure should .not be repeated several times during the Bessemer treatment. In practice, however, it has been found that the most satisfactory results are obtained by limiting these manipulations to adding the, final slag obtained from a charge under Bessemer treatment, and which slagis relatively rich in chromium, to another charge during the earlier stages of-desilication. The preferred procedure is a. follows: When a. Bessemer treatment is.

raccomplished, ithe chromium alloy, which is poor mcarbonand silicon, is tapped oif, but

7 the converter slag, which is rich in chro-' mium, is retained. A propenquantity of molten silico-chromium alloy is then sups plied to th same converter, and a Bessemer treatment is performed until the chromium content of the converter slag has. been re duced to aminimum, whereupon said slag is tapped --ofiand the Bessemer treatment continued. When the desilication of the silico-chromium' alloy has reached. the de- A. Working' according to the method stated in our application 867'. No. 335,670.

Ferro-silico-chromium containing 25% of silicon+chrome ore+lime+free oxygen: ferro-chromium oor in carbon and silicon with of ciiromium-i-slag containing 15% of chromium.

B. Working according to the present process.

(a) The first part of the process.

Ferro-silico-chromium containing 25% of silicon+the final slag (and slag), having 15% ofchromium, from a preceding treatment-f-free -oxygen:ferro-silico-chromium containing 15% of silicon+slag having 3% of silicon, which slag is tapped oif. (b) The latter part of the process. Ferro-silico-chromium containing. 15%

of silicon+chrome ore+lime+ free oxygen :ferro-chromium poor in carbon and. silicon containing 74% of chromium, which is tapped out of the converter,+slag having I 15% of chromium, which is retained in the converter till the next blowing.

. Thus the result of the processes indicated with and togetherz F erro-silico-chromium containing 25% of oxygen:

silicon+chromium+lime+free form-chromium poor in'carbon and silicon having/74% of chromiun1+slag containing 3% of chromium.

'While'it has not been heretofore possible to obtainas a finished alloycmore than of the chromium supplied to the charge under treatment, such alloy being in the form of ferro-silicon-chromium and chrome ore,

by means of the present improvementit is possible to increase the output of chromium Having, "thus described our invention, what we claim is:

'1. Theprocessof producing'chromium alloys having a low content of carbon and silicon, which consists in. subjecting a chromium alloy. 11011 111 silicon, at a-tem- 'peratnre above the melting point of the alloy, to theoxidizing action of free oxygen in a bessemerizing process, thereby to dcsilicate the charge, and adding to said charge during the early stage of desilication a slag obtained from a similar charge at a later stage of desilication.

2. The process of producing chromium alloys having a low content of carbon and silicon, which consists in subjecting a chromium alloy rich'm silicon, at a temperature above the melting point of the alloy. to the oxidizing action of free oxygen in a bessemerizing process, thereby to desilicate the charge, interrupting said process when the sili :on content ofthe alloy is approximately 25%, adding to said charge/a slag obtained from a similar charge at a later stage of desilication, and then continuing the bessemerizing process.

3. The process of producing chromium alloys having a low content of carbon and silicon, which consists in subjecting a chromium alloy rich in silicon, at a temperature above th melting point of the alloy, to the oxidizing action of free oxygen in a bessemerizing process, thereby to desilicate the charge, interrupting said process during the early stage of desilication, adding to said charge a slag obtained from a similar charge at a stage of desilication when the slag contains a chromium content of 15%, and continuing the bessemerizing process.

4. The process of producing chromium alloys having a low content of carbon and silicon, whlch consists in subjecting a chromium alloy rich in silicon, at a temperature above the melting point of the alloy, to the oxidizing action of free oxygen in .a, bessemerizing process, thereby to desilicate the charge, interruptin said process when the silicon content of t e alloy is approximately 25%, adding to said charge a slog containing a chromium content of approximately 15%, and continuing the besse- 15 merizing process.

In testimony whereof we have afiixed our signatures in presence of two witnesses.

BO MICHAEL STUR-E KALLING. SVEN DAGOBERT DANIELI.

Witnesses:

CHR. REoHFRfis, J osnr J OHANSSON. 

